Knowledge of the various parameters of growth and differentiation of facial primordia can provide fundamental information which will permit a more complete understanding of both normal and abnormal development. The goals include: an evaluation of cell proliferation in explanted chicken facial primordia, an evaluation of alterations in mitotic indices in explants of primordia which are epithelial free, quantitative study of differentiation of muscle, cartilage, and olfactory neurons under control and experimental in vitro conditions. These broad goals will be pursued by autoradiographic analysis and comparison of mitotic indices taken from explants of facial primordia prior to overt tissue differentiation and after tissue differentiation. Addition of the growth factors, epidermal growth factor and transferrin, will be used in defined medium in order to assess their role in normal growth of these primordia and in order to define their influence if any on the separate tissues which differentiate. Cell proliferation will also be evaluated in organ culture conditions in which the extracellular matrix of the facial primordia has been altered by inclusion of hyaluronidase into the culture medium. Differentiation of cartilage, muscle and olfactory neurons will be evaluated under the conditions described above. The role of the epithelium in differentiation of these tissues will be assessed by explanation of epithelial-free explants. Quantitative evaluation of the volume of tissues produced under various culture conditions will involve histochemical or immunocytochemical localization of the tissues and computer assisted volume measurements of the total tissues formed under the various circumstances. Three dimensional reconstructions, using computer records of the tissue will permit an evaluation of the morphology of these tissues and comparison between the normal control and experimental situations.